The present invention relates generally to materials treatment and more particularly to a method and apparatus for mechanically removing solid particulates from a fluid stream.
The discipline of separation and purification of solid materials is concerned with development and application of methods and processes in comminution, sorting and concentration or enrichment of primary or secondary raw materials. It encompasses a wide variety of processes including: crushing and milling, screening, sorting, classification, and separation of multiphase and multicomponent systems. The basic processes considered here include solid-gas, solid-liquid, and solid-solid-liquid systems.
Separation of solid particulates from gases or liquids depends on subjecting particles to a certain force which drives them to a collecting surface. The forces may be gravitational, inertial, physical or barrier, or diffusional. One mechanical type device that is commonly used to separate solid particulates from fluids is the cyclone collector. The cyclone collector operates on a centrifugal principle and is widely used for classification and for performing separations in solids-laden gases or slurries. In a cyclone collector the dirty feed stream enters through a tangential inlet into a cylindrical section, setting up a rotational motion and forming a vortex along the inside surface between the underflow and overflow. The stream is fed at sufficiently high velocity so that the centrifugal forces along the walls cause the particles to settle against the walls where they are directed to the underflow. Coincidentally, some fine particles can pass into a secondary vortex and out through the overflow.
Cyclone efficiency, defined at the underflow for each size fraction, can approach 100 percent for coarse particles and 0.0 percent for very fine sizes. Cyclone performance can be reliably predicted in most applications. However, its practical use is restricted to certain operating limits which must be maintained. One such limitation occurs when the solids are too small. Usually when the solids are less than 5 or 10 microns in diameter, separation efficiency for most materials is unsatisfactory. Another limit is that of the fluid and solids density. For good performance, the differential between solids and fluids specific gravities must be sufficient for good separation. Finally, highly viscous fluids do not produce sharp separations.
The present invention relates to an improved method and apparatus for removing very small particulates.
In U.S. Pat. No. 3,257,798 there is disclosed an exhaust treatment apparatus which includes a first cyclonic separator and a second cyclonic separator. The first cyclonic separator divides an exhaust gas mixture into a clean stream and a dirty stream while the second cyclonic separator removes solid particulates from the dirty gas stream emitted from the first cyclonic separator. The clean gas streams from both cyclonic separators are fed into a catalytic converter where they are purified and then exhausted.
In U.S. Pat. No. 3,254,478 there is disclosed a dust collecting apparatus which includes a cyclone type device and wherein the separated gas stream is recycled by an exhauster back to the inlet opening in the cyclone type device.
In U.S. Pat. Nos. 4,001,121, 4,298,359 and 4,460,391 there are disclosed tangential inertial separators wherein the clean gas is removed from the center of the cyclone vortex while the remaining gas and separated solids are exhausted tangentially for further cleanup.
Other known patents of interest are U.S. Pat. Nos. 1,660,865, 1,845,358, 1,845,567, 2,701,056, 2,818,935, 3,095,369 and 3,948,771. In FIGS. 20-103(b) on page 20-87 of Perry's Chemical Engineer Handbook, Fifth Edition, there is shown a mechanical collector with recirculating flow. The collection efficiency of this unit is comparable with that of a cyclone. The centrifugal fields are higher than in a cyclone, but this is compensated by the higher intensity of the secondary flows, with their inherent reentrainment tendencies.
It is an object of this invention to provide a new and improved method and apparatus for removing solid particulates from a fluid stream.
It is another object of this invention to provide a new and improved method and apparatus for removing solid particulates from a fluid stream using inertial type devices.
It is a further object of this invention to provide a method and apparatus for removing solid particulates from a fluid stream using inertia type devices and which has a high separation efficiency, even for submicron size particles.